There are numerous vehicles that are used to haul cargo ranging from commercial fleets of trucks, step vans, panel trucks and the like to do-it-yourself rental trucks that consumers can rent to move or haul various items. In addition there are various types of trailers that are used to haul cargo ranging from semi trailers, to trailers that are used to haul recreational vehicles such as snowmobiles, all terrain vehicles (ATV), person watercraft, motorcycles and the like.
In many instances a ramp is used to load and unload cargo from such vehicles and trailers. Removable ramps are common and are either stored within the cargo compartment of the vehicle or trailed and unload for use and loaded after use. Some vehicles provide for ramps that are stored under the cargo compartment. In other instances, the rear or cargo door of the vehicles and trailers can be pivoted downward and used as a ramp; however, it can be difficult, especially in the case of large, heavy cargo doors, for an individual to lift the cargo door back into its closed position.
Lift assist systems have been developed extensively for pickup truck tailgates as exemplified by U.S. Pat. No. 3,336,070 to Jackson, U.S. Pat. No. 4,143,904 to Cooper et al., U.S. Pat. No. 5,358,301 to Konchan et al., U.S. Pat. No. 5,988,724 to Wolda, U.S. Pat. No. 6,637,796 to Westerdale et al., U.S. Pat. No. 6,769,729 to Bruford et al., U.S. Pat. No. 6,793,263 to Bruford et al., U.S. Pat. No. 6,796,592 to Austin, U.S. Pat. No. 6,846,030 to Koehler et al., U.S. Pat. No. 6,874,837 to Bruford et al., and U.S. Pat. No. 6,905,156 to Miller et al. and U.S. Patent Application Publication Nos. 2004/0178651 to Austin and 2005/0194808 to Austin.
Lift assist systems that have been designed and developed for pickup tailgates are generally not suitable or adaptable for used in conjunction with ramps that are used in conjunction with cargo vehicles and trailers. In this regard, pickup truck tailgates are generally hollow which allows for the lift assist systems to be housed therein, dimensionally constrained only by the cavity within the hollow tailgates. In addition, pickup tailgates are relatively short, perhaps being only about two feet tall so there is not much of a moment arm about the axis of pivot of a tailgate. Also, pickup truck tailgates are only pivoted about 90 degrees between a vertical position and a horizontal position (in which they are supported by various linkage brackets).
The present invention provides for lift assist systems for use with door ramps of trucks and trailers which allows the free end of the door ramps of such vehicles and trailers to move assisted between a vertical position and an inclined position between which positions the door ramps pivots through a obtuse angle of greater than 90 degrees so that the free end of the door ramp rests on the ground.